Nubuck-like artificial leather, and method for producing nubuck-like artificial leather

ABSTRACT

Provided is a nubuck-like artificial leather having a moist feel and nap close to those of natural leather, and superior abrasion resistance. A nubuck-like artificial leather 100 is provided with a flexible sheet 100′ including a base material containing tangled fibers 10 to which a resin 20 is added. Voids 30 are formed in the flexible sheet 100′, the voids 30 being surrounded by cross-sections of the fibers 10 as viewed in a cross-section parallel to a thickness direction of the flexible sheet 100′, and the voids being held by the fibers 10 being bonded together by the resin 20. In a region having a unit area of the cross-section of the flexible sheet 100′, a ratio (A/B) of a cross-sectional area (A) of a continuous structure 40 formed by the fibers 10 being bonded together by the resin 20 to a cross-sectional area (B) of the voids is 15/85-90/10.

TECHNICAL FIELD

The present invention relates to a nubuck-like artificial leatherincluding a flexible sheet obtained by adding a resin to a base materialcontaining tangled fibers, and a method for producing the nubuck-likeartificial leather.

BACKGROUND ART

Nubuck-like artificial leather is desired to have tactile feel andtexture close to those of natural leather. Natural leather contains amoderate amount of voids, which structure provides a characteristictactile feel (a smooth, soft, and supple feel called “moist feel”) andtexture (nap). It is considered that nubuck-like artificial leather thathas a structure (voids) similar to that of natural leather can have amoist feel and nap similar to those of natural leather. Meanwhile,natural leather has a drawback that it easily wears, and therefore,nubuck-like artificial leather is desired to have superior abrasionresistance that cannot be achieved by natural leather. To this end,suitable materials should be selected for nubuck-like artificialleather.

As a technique of producing nubuck-like artificial leather, commonlyknown are a wet method of immersing a fiber sheet impregnated with asolvent-based polyurethane resin in a solidification liquid so that thesolvent-based polyurethane resin is solidified (see, for example, PatentDocument 1), and a dry method of drying a fiber sheet impregnated with awater-based polyurethane resin in a gas phase so that the water-basedpolyurethane resin is solidified (see, for example, Patent Document 2).

Patent Document 1 describes a method for producing a nubuck-like sheetthat includes impregnating a fiber base material with a polycarbonatepolyurethane resin, which is a solvent-based polyurethane resin,immersing the resulting fiber base material in an aqueous dimethylformamide solution so that the polycarbonate polyurethane resin in thefiber base material is solidified, washing the resulting fiber basematerial in hot water, and drying the resulting fiber base material.According to Patent Document 1, the polycarbonate polyurethane resindoes not ooze from the back surface of the sheet, and therefore, thenubuck-like sheet has excellent appearance and texture.

Patent Document 2 describes a method for producing a nubuck-like sheetthat includes impregnating a fiber base material with a W/O urethaneresin, which is a water-based polyurethane resin, thermally drying theresulting base material, and subjecting the resulting base material toembossing and raising. According to Patent Document 2, the raisingallows for formation of a raised region and a non-raised region on thesheet, resulting in a tactile feel and texture close to those of naturalleather.

CITATION LIST Patent Literature

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. H07-42082

Patent Document 2: Japanese Unexamined Patent Application PublicationNo. H07-60885

SUMMARY OF INVENTION Technical Problem

However, the wet method, exemplified by Patent Document 1, and the drymethod, exemplified by Patent Document 2, have the following respectiveproblems. In the nubuck-like sheet of Patent Document 1, voids areformed as an empty space where the solvent (aqueous dimethyl formamidesolution) has been removed from the solvent-based polyurethane resin. Inother words, voids are formed in the solvent-based polyurethane resin.Therefore, when the solvent-based polyurethane resin is worn away fromthe sheet surface by abrasion, etc., the voids also disappear, easilyleading to a deterioration in moist feel and nap. Thus, in thenubuck-like sheet of Patent Document 1, the solvent-based polyurethaneresin having voids formed therein is exposed on the sheet surface and istherefore easily worn away. Therefore, the nubuck-like sheet of PatentDocument 1 has a problem with its durability.

In the nubuck-like sheet of Patent Document 2, the fibers and thewater-based polyurethane resin reinforce each other. Therefore, thenubuck-like sheet of Patent Document 2 is superior to a nubuck-likesheet produced by the wet method in terms of durability. However, in thenubuck-like sheet of Patent Document 2, the water-based polyurethaneresin has high affinity to fibers, and therefore, easily forms a coatingfilm on the surface of the fiber base material. This makes it difficultto impart a sufficient moist feel and nap to the nubuck-like sheet.

Thus, in the conventional art, it is difficult to provide a nubuck-likeartificial leather that has a moist feel and nap close to those ofnatural leather, and at the same time, has high abrasion resistance.With this in mind, the present invention has been made. It is an objectof the present invention to provide a nubuck-like artificial leatherthat has not only a moist feel and nap close to those of natural leatherbut also superior abrasion resistance, and a method for producing thenubuck-like artificial leather.

Solution to Problem

To achieve the above object, a nubuck-like artificial leather accordingto the present invention, comprises:

a flexible sheet including a base material containing tangled fibers,and a resin added to the base material, wherein

voids are formed in the flexible sheet, the voids being surrounded bycross-sections of the fibers as viewed in a cross-section parallel to athickness direction of the flexible sheet, and the voids being held bythe fibers being bonded together by the resin.

According to the nubuck-like artificial leather thus configured, voidssurrounded by cross-sections of the fibers are formed in the flexiblesheet, and in addition, the fibers are bonded together by the resin.Therefore, the voids are distributed in the flexible sheet to a suitableextent and are fixed. Such a structure is similar to that of naturalleather. Therefore, the nubuck-like artificial leather thus configuredcan have a moist feel and nap close to those of natural leather.Furthermore, the fibers in the flexible sheet are reinforced by theresin, and therefore, a strength greater than that of natural leather isprovided, resulting in an artificial leather product having superiorabrasion resistance.

In the nubuck-like artificial leather of the present invention, in aregion having a unit area of the cross-section of the flexible sheet, aratio (A/B) of a cross-sectional area (A) of a continuous structureformed by the fibers being bonded together by the resin to across-sectional area (B) of the voids is preferably 15/85-90/10.

According to the nubuck-like artificial leather thus configured, theratio (A/B) of the cross-sectional area (A) of the continuous structureto the cross-sectional area (B) of the voids is adjusted within asuitable range. Therefore, a well-balanced combination of superiorabrasion resistance attributed to the continuous structure that is notprovided by natural leather, and a moist feel and nap attributed to thevoids that are comparable to those of natural leather, can be provided.

In the nubuck-like artificial leather of the present invention,

the fibers preferably have a mono-fineness of 0.1-0.7 dtex.

According to the nubuck-like artificial leather thus configured, thefibers have a suitable mono-fineness. Therefore, necessary andsufficient abrasion resistance can be provided, and at the same time, aparticularly good nap can be provided.

In the nubuck-like artificial leather of the present invention,

a ratio (a/b) of a length (a) to a diameter (b) of each of the fibers ispreferably 2-1700.

According to the nubuck-like artificial leather thus configured, theratio (a/b) of the length (a) to the diameter (b) of each of the fibersis adjusted within a suitable range. Therefore, necessary and sufficientabrasion resistance can be provided, and at the same time, a good moistfeel and nap can be provided.

In the nubuck-like artificial leather of the present invention,

the resin is preferably at least one selected from the group consistingof polyurethane resins, silicone resins, and acrylic resins.

According to the nubuck-like artificial leather thus configured, theresin is suitably selected. Therefore, the artificial leather productcan have suitable flexibility in addition to superior abrasionresistance.

In the nubuck-like artificial leather of the present invention,

the voids are preferably present in a region of the flexible sheetextending from a front surface of the flexible sheet toward a backsurface of the flexible sheet, the region ranging from a 0-15% region toa 0-40% region, where a position of the front surface of the flexiblesheet is 0%, and a position of the back surface of the flexible sheet is100%.

According to the nubuck-like artificial leather thus configured, thevoids are formed in a suitable region in the flexible sheet. Therefore,necessary and sufficient abrasion resistance can be maintained, and atthe same time, a good moist feel and nap can be provided.

In the nubuck-like artificial leather of the present invention,

a front surface of the nubuck-like artificial leather preferably has asurface roughness of 0.2-1.55 μm.

According to the nubuck-like artificial leather thus configured, thesurface roughness is adjusted within a suitable range. Therefore, anubuck-like nap, and smoothness peculiar to artificial leather, can beprovided.

To achieve the above object, a nubuck-like artificial leather productionmethod according to the present invention, comprising:

an impregnation step of impregnating a base material containing tangledfibers and having a weight of 150-1000 g/m², with 15-40 wt % of a resinwith respect to the weight of the base material in terms of solidcontent; and

a drying step of drying the base material impregnated with the resin at80-150° C. for 50-1200 sec.

According to the nubuck-like artificial leather production method of thepresent invention thus configured, by carrying out the impregnation stepand the drying step under the above conditions, voids surrounded bycross-sections of the fibers are formed in the flexible sheet, and inaddition, the fibers are bonded together by the resin. As a result, thevoids are distributed in the flexible sheet to a suitable extent and arefixed. Such a structure is similar to that of natural leather.Therefore, a moist feel and nap close to those of natural leather can beprovided. Furthermore, the fibers in the flexible sheet are reinforcedby the resin, and therefore, a strength greater than that of naturalleather is provided, resulting in an artificial leather product havingsuperior abrasion resistance.

The nubuck-like artificial leather production method of the presentinvention preferably further comprises:

a finishing step of, after the drying step, finishing the base materialimpregnated with the resin.

According to the nubuck-like artificial leather production method of thepresent invention thus configured, by carrying out the finishing step, amoist feel and nap closer to those of natural leather can be provided.

In the nubuck-like artificial leather production method of the presentinvention,

the drying step is preferably carried out by dry-heat drying ormoist-heat drying.

According to the nubuck-like artificial leather production method of thepresent invention thus configured, by carrying out dry-heat drying ormoist-heat drying on the base material impregnated with the resin, theresin can be reliably solidified in every part including inner parts ofthe base material, resulting in an artificial leather product havingsuperior strength and abrasion resistance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative diagram showing a microscopic internalstructure of a nubuck-like artificial leather according to the presentinvention.

FIG. 2 is a flowchart showing steps of a method for producing thenubuck-like artificial leather of the present invention.

FIG. 3 are SEM images at 1000 times magnification of a cross-sectionparallel to the thickness direction and the front surface of: (a) thenubuck-like artificial leather of the present invention; (b) aconventional artificial leather; and (c) natural leather.

DESCRIPTION OF EMBODIMENTS

Environmental awareness has in recent years gained momentum, andtherefore, in the textile industry, there has been a demand forenvironmentally friendly manufacturing technologies. For nubuck-likeartificial leather, it is expected that the dry method, in which asolvent is basically not used, will go mainstream instead of the wetmethod, in which a large amount of a solvent is used. With this in mind,in the present invention, attention has been paid to the dry method as amethod for producing a nubuck-like artificial leather. In particular,improvements to the conventional dry method, which has a problem with amoist feel and a nap, have been extensively studied. Embodiments of anubuck-like artificial leather according to the present invention and aproduction method therefor will now be described in detail withreference to the accompanying drawings. Note that the present inventionis in no way intended to be limited to the embodiments described below.

(Nubuck-Like Artificial Leather)

FIG. 1 is an illustrative diagram showing a microscopic internalstructure of a nubuck-like artificial leather 100 according to thepresent invention. Note that FIG. 1 is not to scale, i.e., the shapes,sizes, positional relationship, etc., of parts shown in FIG. 1 are notthe same as the actual ones. The nubuck-like artificial leather 100includes a flexible sheet 100′ that is obtained by impregnating a basematerial formed of fibers 10 as a base with a resin 20. Note that thenubuck-like artificial leather 100 may be commercially produced in aform in which a lining or the like is attached to the flexible sheet100′. For the sake of simplicity, the flexible sheet 100′ itself withouta lining or the like being attached thereto is herein regarded as thenubuck-like artificial leather 100.

The base material is a nonwoven fabric formed of a plurality of tangledfibers 10. The weight (per unit area) of the base material is adjustedto 150-1000 g/m². If the weight (per unit area) of the base material isless than 150 g/m², the resin 20 easily passes through the fibers 10included in the base material. If the weight (per unit area) of the basematerial is more than 1000 g/m², it is difficult to sufficientlyimpregnate the base material with the resin 20, i.e., the resin is lesslikely to be held between the fibers 10 included in the base material. Athickness L of the base material is adjusted to 0.5-3.7 mm. If thethickness L of the base material is less than 0.5 mm, a nubuck-likeartificial leather as a final product is less likely to have a moistfeel and a nap, i.e., is likely to have paper-like texture. If thethickness L of the base material is more than 3.7 mm, the workability ofthe base material as an industrial material is likely to deteriorate,leading to problems with its production, such as sewing difficulties,etc. Examples of the fibers 10 in the base material include syntheticfibers, such as polyesters, nylons, acrylic fibers, vinylons, urethanes,etc., semisynthetic fibers, such as acetates, triacetates, Promix, etc.,and regenerated fibers, such as rayons, cupra, polynosic, etc. The abovefibers may be used alone or in combination as commingled fibers. Amaterial for the fibers 10 is preferably polyester, nylon, acrylic, orrayon in terms of versatility and durability, more preferably polyester,which has superior strength.

Examples of the resin 20 include polyurethane resins, silicone resins,and acrylic resins. Of these resins, polyurethane resins are preferable.Polyurethane resins are roughly organized into non-water-basedpolyurethane resins (solvent-based polyurethane resins) and water-basedpolyurethane resins. Although water-based polyurethane resins aresuitably used herein because the present invention is directed to thedry method, non-water-based polyurethane resins for use in theconventional wet method may be used. Note that a method for producingthe nubuck-like artificial leather 100 of the present invention usingthe dry method is described in detail in the section “Method forProducing Nubuck-like Artificial Leather” below. Examples ofpolyurethane resins include polyether polyurethane resins, polyesterpolyurethane resins, polycarbonate polyurethane resins, etc. Thesepolyurethane resins may be used alone or in combination. Of thesepolyurethane resins, polycarbonate polyurethane resins are preferable interms of abrasion resistance. Polyurethane resins are organized, by howthey are cured, into one-part, two-part, and wet-curable polyurethaneresins, etc. Of these polyurethane resins, aqueous one-part polyurethaneresins are preferable because their environmental impact and operationload are small. Examples of aqueous one-part dispersion polyurethaneresins include self-emulsification and forced-emulsificationpolyurethane resins. Note that each of the above polyurethane resins mayadditionally contain various additives, such as catalysts, crosslinkingagents, lubricating agents, gelation accelerating agents, fillers,waxes, light resistance improvers, foaming agents, thermoplastic resins,thermosetting resins, dyes, pigments, flame retardants, electricalconductivity-imparting agents, antistatic agents, moisture permeabilityimprovers, water repellents, oil repellents, hollow foams, waterabsorbents, protein powders, moisture absorbents, deodorants, foamstabilizers, defoamers, antifungal agents, antiseptics, pigmentdispersing agents, inert gases, antiblocking agents, hydrolysisinhibitors, matting agents, tactile feel improvers, thickeners, etc.

The amount of the resin 20 with which the base material is impregnatedis adjusted to 15-40 wt %, preferably 20-30 wt %, with respect to theweight (per unit area) of the base material in terms of solid content.If the amount of the resin 20 with which the base material isimpregnated is less than 15 wt %, the bonding force between the fibers10 is insufficient, and therefore, it is difficult to form voids 30described below, so that a nubuck-like artificial leather as a finalproduct is less likely to have a moist feel. If the amount of the resin20 with which the base material is impregnated is more than 40 wt %, anap is likely to be impaired, leading to a coarse and hard artificialleather.

The nubuck-like artificial leather 100 of the present invention isconfigured to have a structure similar to that of natural leather, whichis a porous material. Specifically, a large number of microscopic spacessurrounded by a plurality of fibers 10 bonded together by the resin 20are formed in the flexible sheet 100′ included in the nubuck-likeartificial leather 100. The microscopic space is herein referred to as avoid 30. In the flexible sheet 100′, the fibers 10 are fixed to eachother by the resin 20 at a portion where the fibers 10 intersect, and inaddition, the resin 20 adheres to the surfaces of the fibers 10 to asuitable extent, and therefore, a continuous structure 40 is formed inwhich the fibers 10 are bonded together by the resin 20. The continuousstructure 40 thus formed substantially fixes a relative positionalrelationship between the fibers 10 in the flexible sheet 100′. As aresult, the form of each void 30 surrounded by the fibers is maintained,and the voids are fixed in the flexible sheet 100′.

As shown in FIG. 1, in the nubuck-like artificial leather 100 of thepresent invention, the voids 30, each of which is surrounded by a largenumber of cross-sections extending perpendicularly to a longitudinaldirection of the fibers 10, are dispersed in the flexible sheet 100′ toa suitable extent. Such a structure is similar to that of naturalleather. As a result, a tactile feel (moist feel) and texture (nap)close to those of natural leather can be provided. In addition, in theflexible sheet 100′, the fibers 10 are reinforced by the resin 20, andtherefore, the strength is greater than that of the natural leather,resulting in superior abrasion resistance.

Various nubuck-like characteristics, such as “moist feel,” “nap,”“abrasion resistance,” etc., that are imparted to the artificialleather, are affected by a state of the presence of the continuousstructure 40 and the voids 30 in the flexible sheet 100′, specifically,the amount of space in the flexible sheet 100′ that is occupied by thecontinuous structure 40 (also referred to as the occupancy rate of thecontinuous structure 40 or the continuous structure occupancy rate).Here, the nubuck-like characteristics can be provided by adjusting aratio A/B within a suitable range, where, in a region having a unit areaof an image of a cross-section of the flexible sheet 100′ captured by anelectronic microscope, “A” represents the cross-sectional area of thecontinuous structure 40, and “B” represents the cross-sectional area ofthe voids 30. Note that “A” (%) corresponds to the occupancy rate of thecontinuous structure 40 in the nubuck-like artificial leather 100. Inthe nubuck-like artificial leather 100 of the present invention, theratio A/B is adjusted to 15/85-90/10, preferably 20/80-80/20. The ratioA/B can be changed by adjusting the amount of the resin 20 with whichthe fibers 10 (base material) are impregnated. In the nubuck-likeartificial leather 100 of the present invention having a ratio A/Bwithin the above range, the continuous structure 40 improves theabrasion resistance of the flexible sheet 100′, and the voids 30 impart,to the flexible sheet 100′, a moist feel and nap comparable to those ofnatural leather. If the ratio A/B is less than 15/85, the relativeproportion of the continuous structure 40 in the flexible sheet 100′ issmall, and voids are excessive, and therefore, the strength of theflexible sheet 100′ is reduced, and the flexible sheet 100′ easilywears. If the ratio A/B is more than 90/10, the relative proportion ofthe continuous structure 40 in the flexible sheet 100′ is large, andvoids are insufficient, and therefore, the elasticity of the flexiblesheet 100′ is lost, and it is difficult to impart a sufficient moistfeel and nap.

In the nubuck-like artificial leather 100 of the present invention, itis not essential that the voids 30 are distributed throughout theflexible sheet 100′. The voids 30 may only need to be present from thefront surface of the flexible sheet 100′ up to a suitable depth. Asshown in FIG. 1, assuming that the position of the front surface of theflexible sheet 100′ is 0%, and the position of the back surface is 100%,a region d where the voids 30 are present may extend from the frontsurface toward the back surface of the flexible sheet 100′, the region dranging from a 0-15% region to a 0-40% region, preferably from a 0-20%region to a 0-35% region. In this case, the nubuck-like artificialleather 100 has a moist feel and nap similar to those of naturalleather, and at the same time, can maintain good abrasion resistance. Ifthe region where the voids 30 are present extends from the front surface(0%) to less than 15% of the flexible sheet 100′, voids areinsufficient, and therefore, the elasticity is lost, and it is difficultto impart a sufficient moist feel and nap. If the region where the voids30 are present is extends from the front surface (0%) to more than 40%of the flexible sheet 100′, voids are excessive, and therefore, thestrength of the flexible sheet 100′ is reduced, and the flexible sheet100′ easily wears.

In the nubuck-like artificial leather 100 of the present invention, tosuitably select or adjust a size of the fibers 10 is effective inproviding a well-balanced combination of a moist feel and nap, andabrasion resistance. The thickness of the fibers 10 that is measured asa mono-fineness is 0.1-0.7 dtex, preferably 0.1-0.5 dtex. If themono-fineness is less than 0.1 dtex, it is difficult to ensuresufficient abrasion resistance. If the mono-fineness is more than 0.7dtex, it is difficult to provide a moist feel and a nap. A ratio a/b(so-called aspect ratio) of a length (a) to a diameter (b) of each ofthe fibers 10 that are measured when a cross-section parallel to thethickness direction of the nubuck-like artificial leather 100 isobserved using a microscope is adjusted to 2-1700, preferably 5-1700,and more preferably 8-1700. If the ratio a/b is less than 2, the fibers10 have an excessively short fiber length, and therefore, it isdifficult to form a sufficient number of portions where the fibers 10intersect, so that the strength of the flexible sheet 100′ is reduced,and the flexible sheet 100′ easily wears. In addition, the nonwovenfabric has an insufficient thickness, and it is difficult to form voids.If the ratio a/b is more than 1700, the fibers 10 has an excessivelylong fiber length, and therefore, portions where the fibers 10 intersectare not uniformly distributed, so that the artificial leather is likelyto have non-uniform color and physical properties. Note that, as long asthe fibers 10 used satisfy the above conditions, the fibers 10 may becommingled fibers including fibers having different sizes.

The nubuck-like artificial leather 100 of the present invention thusconfigured has a porous structure in which the voids 30 are formed andstacked over top of each other in a cross-sectional view taken parallelto the thickness direction. The porous structure is similar to that ofnatural leather, which is a porous material. Therefore, according to thenubuck-like artificial leather 100 of the present invention, a moistfeel and nap close to those of natural leather can be provided.Furthermore, in the nubuck-like artificial leather 100 of the presentinvention, the fibers 10 included in the flexible sheet 100′ arereinforced by the resin 20, and therefore, abrasion resistance superiorto that of natural leather can be provided.

(Method for Producing Nubuck-Like Artificial Leather)

FIG. 2 is a flowchart showing steps of a method for producing thenubuck-like artificial leather of the present invention. A symbol “S”added to each block means a step. The nubuck-like artificial leather ofthe present invention is produced by carrying out a fleece formationstep (S1), a fiber bonding step (S2), an impregnation step (S3), adrying step (S4), and a finishing step (S5) described below. Of thesesteps, the impregnation step (S3) and the drying step (S4) are acharacteristic feature of the present invention. By carrying out the twosteps, a moist feel and nap close to those of natural leather can beprovided, and an artificial leather product having superior abrasionresistance can be obtained. In addition, by carrying out the finishingstep (S5), the moist feel and nap of the nubuck-like artificial leatheras a final product can be further improved. The steps will now bedescribed.

Initially, a base material (nonwoven fabric) that is a base for thenubuck-like artificial leather is prepared. The base material isproduced by the fleece formation step (S1) of forming a layer includinga set of fibers, which is called fleece (may also be called a web), andthe fiber bonding step (S2) of bonding the fibers together using abinder. The fleece formation step is carried out by a technique, such asdrylaying, wetlaying, spunbonding, etc. The fiber bonding step iscarried out by a technique, such as chemical bonding, needle punching,spunlacing, stitch bonding, steam jet, etc. When the fleece formationstep (S1) and the fiber bonding step (S2) are carried out, the amount ofthe fibers and a condition for bonding the fibers are adjusted so thatthe weight (per unit area) of the base material is 150-1000 g/m².

Next, the impregnation step (S3) of impregnating the base material witha resin is carried out. The impregnation step is carried out by amangle-pad technique of immersing a base material in a resin solutioncontaining a resin, and squeezing the base material through a mangle, acoating technique of applying a resin solution to a base material usinga spray coater, a gravure coater, a reverse coater, a doctor-knifecoater, etc. Of these techniques, the mangle-pad technique is preferablebecause a base material can be uniformly impregnated with a resin. Acondition for impregnation with the resin is adjusted so that 30-300g/m² of the resin is added to the base material having a weight (perunit area) of 150-1000 g/m² in terms of solid content. As a result, theresin adheres to portions where the fibers intersect. In addition, theresin adheres to the surfaces of the fibers to a suitable extent. Theamount of the resin added to the base material is adjusted to 15-40 wt%, preferably 20-30 wt %, in terms of solid resin content.

Next, the drying step (S4) of drying the base material impregnated withthe resin is carried out. The drying step is carried out by a technique,such as dry-heat drying using a pintenter, a loop dryer, a net dryer, anoven, etc., moist-heat drying using a high-temperature steamer, ahigh-pressure steamer, etc., drying using infrared, drying usingmicrowaves, etc. Of these techniques, dry-heat drying and moist-heatdrying are preferable because the resin can be reliably solidified inevery part including inner parts of the base material. The base materialdried by dry-heat drying or moist-heat drying can be processed into anartificial leather product having superior strength and abrasionresistance. As a condition for drying of the base material, the dryingtemperature is adjusted to 80-150° C., preferably 100-130° C. If thedrying temperature is less than 80° C., the resin is insufficientlydried (cured), and therefore, the resin migrates and has difficulty inadhering to a predetermined position of the fiber. If the dryingtemperature is more than 150° C., the moist feel of a nubuck-likeartificial leather as a final product is reduced, and the nap is likelyto be coarse and hard. The drying time is adjusted to 50-1200 sec,preferably 100-600 sec. If the drying time is less than 50 sec, theresin is insufficiently dried (cured), and therefore, the resin migratesand has difficulty in adhering to a predetermined position of the fiber.If the drying time is more than 1200 sec, the moist feel of anubuck-like artificial leather as a final product is reduced, and thenap is likely to be coarse and hard. After completion of the dryingstep, the fibers in the base material are bonded by the resin and arethereby hardened, and therefore, the base material can be directly usedas a flexible sheet for a nubuck-like artificial leather. In theflexible sheet, formed are a large number of voids surrounded by thefibers. In other words, in the nubuck-like artificial leather of thepresent invention, voids are distributed in the flexible sheet to asuitable extent, and therefore, a structure similar to that of naturalleather is formed.

Finally, the finishing step (S5) of finishing the flexible sheet iscarried out. The finishing step is any suitable step that is carried outif necessary, including a raising process of raising the front surfaceof the flexible sheet. By carrying out the finishing step, the frontsurface of the finished nubuck-like artificial leather has a suitablefriction coefficient (MIU) and surface roughness (SMD), and therefore, amoist feel and nap closer to those of natural leather can be provided.The friction coefficient of the front surface of the nubuck-likeartificial leather is preferably 0.15-0.35, more preferably 0.20-0.30.If the friction coefficient is less than 0.15, the abrasion resistanceis likely to be insufficient. If the friction coefficient is more than0.35, the moist feel is likely to be insufficient. The surface roughnessof the front surface of the nubuck-like artificial leather is preferably0.2-1.55 μm, more preferably 0.2-1.4 μm, and even more preferably0.3-1.2 μm. If the surface roughness of the front surface is less than0.2 μm, the nubuck-like nap is likely to be insufficient. If the surfaceroughness of the front surface is more than 1.55 μm, smoothness peculiarto artificial leather is likely to be impaired.

In the raising process for the flexible sheet, for example, a rolleraround which card clothing or sandpaper (emery) is wrapped (a cardclothing raising machine, an emery raising machine, etc.) can be used.The raising process using a roller is performed by bringing the flexiblesheet into contact with the surface of the roller while moving theflexible sheet in the roller rotating direction (the longitudinaldirection of the flexible sheet). In this case, the raised state of theflexible sheet can be adjusted by changing conditions, such as the typeof card clothing or sandpaper, the rotational speed of the roller, thecontact pressure of the flexible sheet on the roller, the frequency ofcontact of the flexible sheet with the roller, etc.

EXAMPLES

Examples of the nubuck-like artificial leather of the present inventionwill now be described. In these examples, nubuck-like artificialleathers having a characteristic feature of the present invention wereproduced. As comparative examples, artificial leathers that do not haveany characteristic feature of the present invention were produced. Thenubuck-like artificial leathers according to Examples 1-5 and theartificial leathers according to Comparative Examples 1 and 2 wereproduced by the following procedures.

Example 1

A nonwoven fabric (3071A, manufactured by Asahi Kasei FibersCorporation) that includes a mixture of first polyester fibers(mono-fineness: 0.10 dtex) and second polyester fibers (mono-fineness:0.15 dtex) at a weight ratio of 50:50, and has a weight (per unit area)of 269.6 g/m² and a thickness of 0.75 mm, was used. The nonwoven fabricwas dyed using a disperse dye. Thereafter, the front surface of thenonwoven fabric was subjected to a buffing process. Thereafter, thenonwoven fabric was impregnated with a polyurethane resin liquid using amangle-pad technique. The polyurethane resin liquid contained 25 wt % ofa water-based polyurethane resin (SAD8•2 (solid content: 40 wt %),forced-emulsification type, manufactured by DKS Co. Ltd.), and 75 wt %of water. After the impregnation of the nonwoven fabric with thepolyurethane resin liquid using a mangle-pad technique, the nonwovenfabric was subjected to dry-heat drying (thermal treatment) using apintenter at 130° C. for 150 sec. Thus, a flexible sheet including thenonwoven fabric to which a polyurethane resin was added was formed. Theamount of the polyurethane resin added to this flexible sheet was 62g/m² in terms of solid content. Thereafter, the front surface of theflexible sheet was further subjected to a buffing process. Thus, theproduction of the nubuck-like artificial leather of Example 1 wascompleted.

Example 2

A nonwoven fabric (3007B, manufactured by Asahi Kasei FibersCorporation) that includes a mixture of first polyester fibers(mono-fineness: 0.15 dtex) and second polyester fibers (mono-fineness:0.30 dtex) at a weight ratio of 50:50, and has a weight (per unit area)of 273.1 g/m² and a thickness of 0.75 mm, was used. The nonwoven fabricwas dyed using a disperse dye. Thereafter, the front surface of thenonwoven fabric was subjected to a buffing process. Thereafter, thenonwoven fabric was impregnated with a polyurethane resin liquid using amangle-pad technique. The polyurethane resin liquid was the same as thatwhich was used in Example 1. After the impregnation of the nonwovenfabric with the polyurethane resin liquid using a mangle-pad technique,the nonwoven fabric was subjected to dry-heat drying (thermal treatment)using a pintenter at 130° C. for 150 sec. Thus, a flexible sheetincluding the nonwoven fabric to which a polyurethane resin was addedwas formed. The amount of the polyurethane resin added to this flexiblesheet was 50 g/m² in terms of solid content. Thereafter, the frontsurface of the flexible sheet was further subjected to a buffingprocess. Thus, the production of the nubuck-like artificial leather ofExample 2 was completed.

Example 3

A nonwoven fabric (3007B, manufactured by Asahi Kasei FibersCorporation) that includes polyester fibers (mono-fineness: 0.50 dtex),and has a weight (per unit area) of 273.1 g/m² and a thickness of 0.75mm, was used. The nonwoven fabric was dyed using a disperse dye.Thereafter, the front surface of the nonwoven fabric was subjected to abuffing process. Thereafter, the nonwoven fabric was impregnated with apolyurethane resin liquid using a mangle-pad technique. The polyurethaneresin liquid was the same as that which was used in Example 1. After theimpregnation of the nonwoven fabric with the polyurethane resin liquidusing a mangle-pad technique, the nonwoven fabric was subjected todry-heat drying (thermal treatment) using a pintenter at 130° C. for 150sec. Thus, a flexible sheet including the nonwoven fabric to which apolyurethane resin was added was formed. The amount of the polyurethaneresin added to this flexible sheet was 22 g/m² in terms of solidcontent. Thereafter, the front surface of the flexible sheet was furthersubjected to a buffing process. Thus, the production of the nubuck-likeartificial leather of Example 3 was completed.

Example 4

A nonwoven fabric that is the same as that used in Example 3(mono-fineness: 0.50 dtex, weight (per unit area): 273.1 g/m², andthickness: 0.75 mm) was dyed using a disperse dye. Thereafter, the frontsurface of the nonwoven fabric was subjected to a buffing process.Thereafter, the nonwoven fabric was impregnated with a polyurethaneresin liquid by a mangle-pad technique. The polyurethane resin liquidcontained wt % of a water-based polyurethane resin (SAD8•2 (solidcontent: 40 wt %), forced-emulsification type, manufactured by DKS Co.Ltd.), 14 wt % of a dry-heat gelling agent (10-wt % aqueous ammoniumacetate solution), and 61 wt % of water. After the impregnation of thenonwoven fabric with the polyurethane resin liquid using a mangle-padtechnique, the nonwoven fabric was subjected to moist-heat drying(thermal treatment) using high-pressure steam at 130° C. for 600 sec.This set of impregnation with the polyurethane resin liquid andmoist-heat drying (thermal treatment) was performed a total of twotimes. Thus, a flexible sheet including the nonwoven fabric to which apolyurethane resin was added was formed. The amount of the polyurethaneresin added to this flexible sheet was 43 g/m² in terms of solidcontent. Thereafter, the front surface of the flexible sheet was furthersubjected to a buffing process. Thus, the production of the nubuck-likeartificial leather of Example 4 was completed.

Example 5

A nonwoven fabric that is the same as that used in Example 1 (a mixtureof fibers having a mono-fineness of 0.10 dtex and fibers having amono-fineness of 0.15 dtex at a weight ratio 50:50, weight (per unitarea): 269.6 g/m², and thickness: 0.75 mm) was dyed using a dispersedye. Thereafter, the front surface of the nonwoven fabric was subjectedto a buffing process. Thereafter, the nonwoven fabric was impregnatedwith a polyurethane resin liquid by a mangle-pad technique. Thepolyurethane resin liquid contained 50 wt % of a water-basedpolyurethane resin (SAD8•2 (solid content: 40 wt %),forced-emulsification type, manufactured by DKS Co. Ltd.), 27.5 wt % ofa dry-heat gelling agent (10-wt % aqueous ammonium acetate solution),and 22.5 wt % of water. After the impregnation of the nonwoven fabricwith the polyurethane resin liquid using a mangle-pad technique, thenonwoven fabric was subjected to moist-heat drying (thermal treatment)using high-pressure steam at 130° C. for 600 sec. This set ofimpregnation with the polyurethane resin liquid and moist-heat drying(thermal treatment) was performed a total of two times. Thus, a flexiblesheet including the nonwoven fabric to which a polyurethane resin wasadded was formed. The amount of the polyurethane resin added to thisflexible sheet was 72 g/m² in terms of solid content. Thereafter, thefront surface of the flexible sheet was further subjected to a buffingprocess. Thus, the production of the nubuck-like artificial leather ofExample 5 was completed.

Comparative Example 1

A nonwoven fabric that is the same as that used in Example 1 (a mixtureof fibers having a mono-fineness of 0.10 dtex and fibers having amono-fineness of 0.15 dtex at a weight ratio 50:50, weight (per unitarea): 269.6 g/m², and thickness: 0.75 mm) was dyed using a dispersedye. Thereafter, the front surface of the nonwoven fabric was subjectedto a buffing process. The resulting artificial leather was ComparativeExample 1. In other words, the artificial leather of Comparative Example1 is the nubuck-like artificial leather of Example 1 in which thenonwoven fabric is not impregnated with a polyurethane resin liquid.

Comparative Example 2

A nonwoven fabric that is the same as that used in Example 2 (a mixtureof fibers having a mono-fineness of 0.15 dtex and fibers having amono-fineness of 0.30 dtex at a weight ratio 50:50, weight (per unitarea): 273.1 g/m², and thickness: 0.75 mm) was dyed using a dispersedye. Thereafter, the front surface of the nonwoven fabric was subjectedto a buffing process. The resulting artificial leather was ComparativeExample 2. In other words, the artificial leather of Comparative Example2 is the nubuck-like artificial leather of Example 2 in which thenonwoven fabric is not impregnated with a polyurethane resin liquid.

Reference Example 1

Natural leather (real leather nubuck) was prepared as Reference Example1 in order to compare it with the nubuck-like artificial leathers ofExamples 1-5 and the artificial leathers of Comparative Examples 1 and2.

Next, various characteristics of each of the above leathers were checkedby various measurements and evaluations. Based on the results,relationships between the structures and the characteristics of theleathers were studied. The characteristics that were measured andevaluated are the following.

[Occupancy Rate of Continuous Structures, Voids, or Fibers]

Images of cross-sections parallel to the longitudinal direction (Xdirection) and the width direction (Y direction) of each leather werecaptured using a scanning electron microscope (S-3000N, manufactured byHitachi High-Technologies Corporation) at 1000 times magnification. Thesum of the areas of continuous structures, voids, or fibers contained inan SEM image was calculated by image analysis. The proportion of the sumof the areas of continuous structures, voids, or fibers to the area ofthe entire SEM image, which is 100, is referred to as the occupancy rate(%) of continuous structures, voids, or fibers included in each leather.The calculation of the occupancy rate of continuous structures, voids,or fibers was performed for two cross-sections parallel to the Xdirection and two cross-sections parallel to the Y direction of eachleather (a total of four cross-sections), and the occupancy rate wasdefined as the average thereof. FIG. 3 shows SEM images at 1000 timesmagnification of a cross-section parallel to the thickness direction (aregion where voids are formed) and the front surface of: (a) thenubuck-like artificial leather of the present invention (correspondingto Example 1); (b) a conventional artificial leather (corresponding toComparative Example 1); and (c) natural leather (corresponding toReference Example 1).

[Region where Voids are Formed]

An image of a cross-section parallel to the thickness direction of eachleather, extending from the front surface to the back surface, wascaptured using a scanning electron microscope at 1000 timesmagnification. A region where voids were formed was identified from theSEM image. The calculation of the region where voids were formed wasperformed for two cross-sections parallel to the X direction and twocross-sections parallel to the Y direction of each leather (a total offour cross-sections), and the region was defined as the average thereof.

[Aspect Ratio]

Images of cross-sections parallel to the longitudinal direction (Xdirection) and the width direction (Y direction) of each leather werecaptured using a microscope (VHX-200, manufactured by KeyenceCorporation) at 500 times magnification. An aspect ratio (a/b) of alength (a) and a diameter (b) of a fiber included in each leather wascalculated. The calculation of the aspect ratio was performed for twocross-sections parallel to the X direction and two cross-sectionsparallel to the Y direction of each leather (a total of fourcross-sections), and the aspect ratio was defined as the averagethereof.

[Friction Coefficient and Surface Roughness]

A friction coefficient (MIU) and a surface roughness (SMD) in thelongitudinal direction (X direction) of the front surface of eachleather were measured using an automated surface tester (KES-FB4-AUTO-A,manufactured by Kato Tech Co., Ltd.). The measurement of the frictioncoefficient and the surface roughness was performed at three points ofeach leather, and the friction coefficient and the surface roughnesswere defined as the respective averages thereof.

[Tactile Feel]

The tactile feel of each artificial leather was evaluated by sensorytesting according to the following criteria, in which each artificialleather was compared with the natural leather of Reference Example 1.

5: A soft texture and moist feel equivalent to those of natural leatherare recognized

4: A soft texture equivalent to that of natural leather, and a slightlyinferior moist feel, are recognized

3: A texture slightly coarser and harder than natural leather, and aslightly inferior moist feel, are recognized

2: A texture slightly coarser and harder than natural leather isrecognized, and no moist feel is recognized

1: A texture coarser and harder than natural leather is recognized, andno moist feel is recognized

[Appearance]

The appearance of each artificial leather was evaluated by sensorytesting according to the following criteria, in which each artificialleather was compared with the natural leather of Reference Example 1.

5: Soft fine fibers and minute pits and bumps similar to those ofnatural leather are recognized

4: Soft fine fibers similar to those of natural leather are recognized,and no minute pits and bumps are recognized

3: Fibers are recognized, and the fibers appear coarse

2: Long or very short fibers lying flat are recognized

1: A nap totally different from that of natural leather is recognized

[Abrasion Resistance]

A sample extending in the longitudinal direction (X direction) by 300 mmand in the width direction (Y direction) by 70 mm was extracted fromeach leather. A urethane foam having a length of 300 mm, a width of 70mm, and a thickness of 10 mm, was attached to the back surface of thesample. An abrasion test was conducted on the resulting samples. In theabrasion test, a plane abrasion tester (T-type, manufactured by DaieiKagaku Seiki Mfg. Co., Ltd.) was used. Each sample was pressed against arubbing finger covered with cotton canvas with a load of 9.8 N. In thissituation, the sample was abraded by the rubbing finger being moved backand forth across a 140-mm section in the longitudinal direction of thefront surface of the sample at a speed of 60 round-trips per minute.Each time the number of round-trips of the rubbing finger reached 2500,the cotton canvas was replaced. A total of 10,000 round-trips were madeto abrade the sample. After the end of the abrasion test, a condition ofthe sample was visually checked. The abrasion resistance of each leatherwas evaluated according to the following criteria.

Circle: The condition of the front surface remain unchanged

Triangle: It is recognized that the fibers partially come off the frontsurface

Cross: Most of the fibers on the front surface come off

The results of the measurement and evaluation are shown in Table 1below.

TABLE 1 Comparative Comparative Reference Example 1 Example 2 Example 3Example 4 Example 5 Example 1 Example 2 Example 1 Occupancy rate of 71.556.2 46.4 54.3 59.9 — — — continuous structure (%) Occupancy rate of28.5 43.8 53.6 45.7 40.1 — — — voids (%) Occupancy rate of fibers 31.435.8 38.0 38.0 31.9 31.4 35.8 — (%) Void-containing region (%) 26.4 32.319.9 25.4 32.4 — — — Aspect ratio (a/b) 30.9 17.2 13.3 13.3 30.9 30.917.2 Friction coefficient 0.260 0.303 0.320 0.290 0.272 0.327 0.3350.228 Surface roughness (μm) 0.570 0.710 1.544 0.833 0.555 2.238 1.6970.335 Tactile feel 4~5 4 3 3~4 4~5 2 2 5 Appearance 4~5 4 3 3~4 4~5 2~32 5 Abrasion resistance ∘ ∘ ∘ ∘ ∘ ∘ ∘ ×

The nubuck-like artificial leathers of Examples 1, 2, 4, and 5 had afriction coefficient and surface roughness close to those of the naturalleather of Reference Example 1. As a result, their tactile feel andappearance were rated high, and their abrasion resistance was also good.The nubuck-like artificial leather of Example 3 had a slightly greatsurface roughness, but its tactile feel and texture were not such that apractical problem may arise, and its abrasion resistance was good. Incontrast to this, the artificial leathers of Comparative Examples 1 and2 had a friction coefficient and surface roughness much greater thanthose of the natural leather of Reference Example 1. Their abrasionresistance was good because they were artificial leather, but theirtactile feel and appearance were rated low.

The SEM images of FIG. 3 demonstrate that the nubuck-like artificialleather of the present invention has a structure similar to that ofnatural leather. It is considered that such a structure is attributed toa moist feel and nap close to those of natural leather. In addition, thefibers included in the flexible sheet are reinforced by the resin.Therefore, the nubuck-like artificial leather of the present inventionhas a strength greater than that of natural leather, and therefore, hassuperior abrasion resistance.

INDUSTRIAL APPLICABILITY

The nubuck-like artificial leather of the present invention, and themethod for producing the nubuck-like artificial leather, are applicableto various leather products, such as automotive seats, aircraft seats,watercraft seats, sofas, furniture, bags, shoes, etc.

REFERENCE SIGNS LIST

-   -   10 FIBER    -   20 RESIN    -   30 VOID    -   40 CONTINUOUS STRUCTURE    -   100 NUBUCK-LIKE ARTIFICIAL LEATHER    -   100′ FLEXIBLE SHEET

What is claimed is:
 1. A nubuck-like artificial leather comprising: aflexible sheet including a base material containing tangled fibers, anda resin added to the base material, wherein voids are formed in theflexible sheet, the voids being surrounded by cross-sections of thefibers as viewed in a cross-section parallel to a thickness direction ofthe flexible sheet, and the voids being held by the fibers being bondedtogether by the resin.
 2. The nubuck-like artificial leather accordingto claim 1, wherein in a region having a unit area of the cross-sectionof the flexible sheet, a ratio (AB) of a cross-sectional area (A) of acontinuous structure formed by the fibers being bonded together by theresin to a cross-sectional area (B) of the voids is 15/85-90/10.
 3. Thenubuck-like artificial leather according to claim 1, wherein the fibershave a mono-fineness of 0.1-0.7 dtex.
 4. The nubuck-like artificialleather according to claim 1, wherein a ratio (a/b) of a length (a) to adiameter (b) of each of the fibers is 2-1700.
 5. The nubuck-likeartificial leather according to claim 1, wherein the resin is at leastone selected from the group consisting of polyurethane resins, siliconeresins, and acrylic resins.
 6. The nubuck-like artificial leatheraccording to claim 1, wherein the voids are present in a region of theflexible sheet extending from a front surface of the flexible sheettoward a back surface of the flexible sheet, the region ranging from a0-15% region to a 0-40% region, where a position of the front surface ofthe flexible sheet is 0%, and a position of the back surface of theflexible sheet is 100%.
 7. The nubuck-like artificial leather accordingto claim 1, wherein a front surface of the nubuck-like artificialleather has a surface roughness of 0.2-1.55 μm.
 8. A nubuck-likeartificial leather production method, comprising: an impregnation stepof impregnating a base material containing tangled fibers and having aweight of 150-1000 g/m², with 15-40 wt % of a resin with respect to theweight of the base material in terms of solid content; and a drying stepof drying the base material impregnated with the resin at 80-150° C. for50-1200 sec.
 9. The nubuck-like artificial leather production methodaccording to claim 8, further comprising: a finishing step of, after thedrying step, finishing the base material impregnated with the resin. 10.The nubuck-like artificial leather production method according to claim8, wherein the drying step is carried out by dry-heat drying ormoist-heat drying.